The Dreamliner dreams on

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WITH its curvaceous body, large windows, and improved cabin pressure and humidity, the new Boeing 787 (Dreamliner) was to be the answer to the travelling public’s prayers. As the first major airliner to use lightweight composite materials for most of its construction, the 787 Dreamliner also promised 20% better fuel economy and 30% lower maintenance costs.

The airlines bought the hype—even though the technical hurdles to building a carbon-composite airliner were formidable. No fewer than 56 carriers rushed to order the “plastic fantastic” plane after its announcement in January 2005. With 866 aircraft on order, the 787 Dreamliner became the fastest-selling wide-body jet in history.

But thanks to one technical glitch after another, the new plane is running way behind schedule. Today, it is known increasingly as the “Dream-on-liner”. Originally due in 2007, its initial delivery (to All Nippon Airways) won’t now take place until 2011 at the earliest.

The latest delay looks like the most serious yet. In May, routine bending tests in the workshop showed the wing structure to have separated from its skin (“delaminated”) at 120%-130% of the load limit. To pass muster with the Federal Aviation Administration and other certification bodies, wings have to sustain at least 150% of the load limit without rupturing.

Then, in late June, Boeing announced it was postponing the plane’s maiden flight—originally scheduled for June 30th—while it found a way to reinforce the structure where the wings join the fuselage. The 787 Dreamliner’s first flight has now been put off until this autumn or later.

Boeing declared at the time that the fix was relatively simple. Scott Fancher, the Dreamliner’s programme chief, said all that was needed was “a simple modification” using “a handful of parts”. But Gulliver thinks Boeing is in bigger trouble than it admits—and is having to rerun fresh batches of its computer simulations of the wing’s design.

For instance, the Chicago Tribune noted on June 24th that:
The glitch calls into question the accuracy of the complex computer models Boeing used to design the aircraft and to predict how it would respond to flight stresses.

Further digging by the media has cast even more doubt on Boeing’s initial response to the problem. After interviewing two engineers with knowledge of Boeing’s problems, the Seattle Times reported last week that:

The structural flaw that delayed the first flight of the 787 Dreamliner is more complex than originally described by the company, and the plane’s inaugural takeoff is likely at least four to six months away.
Both engineers said the issue requires a thorough redesign of the plane’s wing-to-body join, and the necessary parts will be very difficult to install on the test airplanes that have already been built.

The problem is caused by excessive loads at the ends of the “stringers” on the upper wing skins. Stringers are long rods shaped like I-beams that run the length of the wing, from the root to the tip, to brace the inside of the skin. When the wing bends under load, the upper stringers are compressed, causing stresses to build up where they are attached to the wing’s skin.

The Seattle Times continued:

Excessive loads at stringer ends (known to engineers as ‘runouts’) is not something that should have struck Boeing out of the blue.

The problem with stringer runouts has been identified in the past and recognised as a problem. The issue has arisen on other composite airplanes. Indeed, the stress point at the end of the 787 stringers showed up as a ‘hot spot’ in Boeing’s computer models before the delamination in the wing bend test—but for some reason was never addressed.

Not for the first time have fingers been pointed at the deterioration of Boeing’s engineering excellence. Plane Talking, a blog, put it bluntly:

The current management of Boeing has so gutted the human resource in design and fabrication that it commanded in its glory days that it couldn’t even put the right bolts into the right holes in a sub-fleet of test aircraft, the first of which it doesn’t dare fly—a situation it acknowledged only days after bald-faced assurances that the jet would fly by June 30th.

For their part, the mistake the airlines made was to take Boeing at face value when it swore the spinning and weaving technology for making the carbon-composite Dreamliner held no surprises. The material’s virtue was supposed to be its strength and lightness—features that would translate directly into lower operational costs.

Unfortunately, the weight savings haven’t been anything like those promised. And now the latest modifications needed for strengthening the Dreamliner’s wing roots will detract from them even further.

(Photo credit: Boeing Image)